Ukrainian troops tightened the forces around the major insurgent-held eastern city of Slovyansk but pro-Russia militias struck out elsewhere. Up to 30 pro-Russian militants have been killed in the clashes, the Ukrainian government said.

Meanwhile, 14 Ukrainian soldiers were killed and 66 wounded, officials from the State Security Service said Tuesday.

"The threat now is that we are reaching the point of no return â?? a moment when the escalation cannot be stopped anymore and we literally are on the threshold of a war in Eastern Europe," German Foreign Minister Frank-Walter Steinmeier told Frankfurter Allgemeine Zeitung, a German daily newspaper.

The separatists have held key administration buildings in several cities in Ukraine's east for weeks. In Slovyansk, the separatists' stronghold in the eastern Ukrainian, the Ukrainian military has blockaded the town, trying to reclaim it.

One separatist leader, Myroslav Rudenko, told Russian LifeNews network that 20 people were killed during the counterterrorist operation, some of them civilians who had not participated in the revolt. Ukrainian officials denied the claim.

"The Ukrainian military cannot shoot at civilians," said Avakov. "This limitation is often being used by the enemy to their advantage."

"We are bound hand and foot with the fact that (the separatists) are hiding behind civilians," Avakov said in Slovyansk.

Ukraine's State Security Service said that the civilians in the east are under "serious influence of propaganda and don't trust the actions of Ukrainian law enforcement aimed at destroying terrorists only."

The militants say they want to hold a referendum May 11 on whether to join Russia, whose military has infiltrated Ukraine and has been assisting ethnic Russians who have forced their way into city offices. Though many in eastern Ukraine do want to secede, many have said they do not.

Russain President Vladimir Putin supports the referendum and is also opposing Ukraine's national elections set for May 25. In a referendum on March 16, Ukraine's southern region of Crimea allegedly voted to separate from Ukraine and was then annexed by Russia. The United States said the vote was rigged.

In Donetsk, approximately 75 miles south of Slovyansk, flights from the local airport were suspended Tuesday. Many also expect increased tensions during celebrations marking Victory Day on May 9.

"With parades and rallies traditionally held on May 9, the situation will be perfect for instigating the street clashes," said Nataliya Huseva of Donetsk, which is the center of troubled eastern region. "If I have to go outside on this day, I'll be extremely careful and will stay away from city center."

Huseva said he is especially nervous because of what happened in Odessa, she said. Street clashes between pro-Ukrainian and pro-Russian activists resulted in 46 deaths after some of the activists became trapped by shooting and in a fire.

Ukraine replaced the acting governor of the Odessa region with Ihor Palytsya, a member of parliament. There is concern that Odessa could be the next region to fall to pro-Russia forces. The government sent an elite national guard force to Odessa, where it could be seen Tuesday patrolling the streets.

"(The separatists) have some of the population on their side and with time the population might become more supportive of some kind of new status quo â?? in that sense it is getting harder and harder for the government in Kiev," said Susan Stewart, deputy head of Research Division on Eastern Europe and Eurasia of the German Institute for International and Security Affairs in Berlin.

"I think that there is a chance to regaining control but it would require a certain price to be paid, also in terms of lives."

Russia said that it will move to bolster its Black Sea naval fleet with additional warships and submarines, according to the Interfax news agency, citing comments made by Russian Defense Minister Sergei Shoigu.

You will automatically receive the MyCentralJersey.com Top 5 daily email newsletter. If you don't want to receive this newsletter, you can change your newsletter selections in your account preferences.